Zoom lens

ABSTRACT

A lens of variable equivalent focal length where two lens groups located on either side of an aperture defining means move relative to the aperture defining means, and a lens group of positive power is positioned close to the aperture defining means. The aperture defining means and the associated positive power group may either be stationary or move with change in equivalent focal length.

.Iadd.FIELD OF THE INVENTION .Iaddend.

This invention relates to zoom lenses, and more particularly relates tosuch lenses having a range of equivalent focal lengths which subtend thedimension of the diagonal of the image plane of the lens.

.Iadd.BACKGROUND OF THE INVENTION .Iaddend.

A lens having an equivalent focal length less than the diagonal of itsimage plane may be classified as a wide angle lens. Zoom lenses whichhave a range from wide angle to a long focus or so-called telephotoequivalent focal length (EFL) present different design criteria whenconsidered from the extremes of the EFL's.

A wide angle lens of about 70° field is not difficult to design. Suchdesign generally includes a negative front group and a positive reargroup where the back focal length of the lens is greater than the EFL.Such lens is often termed a retrofocus or reverse telephoto lens. Anexample of an excellent optic of this category is shown in U.S. Pat. No.4,099,849 and is marketed as a Vivitar Series I, 28 mm f/1.9 lens. Onthe other hand, lenses having an EFL several times the diagonal of theimage frame present other design considerations. Examples of a wellcorrected telephoto lens are given in U.S. Pat. No. 3,942,876, and havebeen marketed as Vivitar Series I lenses at 135 mm f/2.3, and 200 mmf/3.0. A comparison of such lens shows completely different designconfigurations and considerations.

Where the EFL range of a zoom lens is to cross the so-called wide angledefinition, a more sophisticated lens design is demanded requiring morelens elements and movements of various lens groups. An example is shownin U.S. Pat. No. 3,975,089, and has been marketed as a Vivitar Series I35-85 mm f/2.8 lens.

Few zoom lenses have been designed and marketed having a lower EFL inthe wide angle range and having a zoom range of greater than 3:1, andthen the actual EFL extremities are subject to a five percent markingtolerance. In such zoom lenses, the spherical .[.abberrations.]..Iadd.aberrations .Iaddend.become excessive as the longer EFL isattempted to be increased and/or attempt is made to increase therelative aperture.

Without size and cost constraints, these problems can be overcome by anyexperienced optical designer. However, there are presently few, if any,commercially acceptable zoom lenses, from the standpoint of compactsize, relative aperture, zoom range, and good quality available from awide angle range with a rated zoom range of three to one or over for the24×36 mm image frame format.

However, Ellis I. Betensky in U.S. patent application Ser. No. 070,749,now U.S. Pat. No. 4,299,454, has disclosed a new configuration for azoom lens which permits a zoom range of almost five to one from a fieldangle of over seventh degrees. Such lenses comprise a front positivegroup, a strong negative second group, a third positive group and insome cases, a fourth positive group. Three of these groups may bemovable to vary the EFL of the lens.

The present invention provides an improvement over and to the foregoingBetensky lens in that it permits a larger aperture for a given physicalsize of the lens, or alternatively a reduction in physical size for agiven relative aperture.

.Iadd.SUMMARY OF THE INVENTION .Iaddend.

Briefly stated, the invention provides a zoom lens comprising a frontpositive group, a second negative group and a rear positive group inwhich a positive power lens group is positioned very closely adjacentthe aperture defining means between the second and rear groups. The lensand aperture defining means may be stationary, or may move in fixedspaced relation as the EFL is varied. This positive optical power at theaperture permits a larger relative aperture by alleviating the limitingfactor of spherical aberration at the longer EFL's. The positivecomponent reduces the marginal ray height of the ray bundle at and pastthe aperture defining means. The optical power of this positive group isrelated to other parameters of the lens as hereinafter described.

A first embodiment of a lens embodying the invention comprises a firstpositive group, a second negative group, the aperture defining meansfollowed by a third positive group in fixed relation to the aperturedefining means, and a fourth positive group. During variation of focallength, the first and fourth groups move simultaneously in one directionand the second group moves in the opposite direction; for focusing allgroups move in fixed relation. In .[.a.]. another embodiment of theinvention, the aperture defining means and the third group move in fixedrelation, and only the first group moves for focusing.

An object of this invention is to provide a new and improved zoom lensof the type described of compact size and/or large relative aperture.

The features of the invention which are believed to be novel areparticularly pointed out and distinctly claimed in the concludingportion of this specification. However, the invention both as to itsorganization and operation together with further objects and advantagesthereof may best be appreciated by reference to the following detaileddescription taken in conjunction with the drawings.[., inwhich:.]..Iadd..

.Iadd.BRIEF DESCRIPTION OF THE DRAWINGS .Iaddend.

FIGS. 1 and 1a are schematic side elevations of one lens form embodyingthe invention; and

FIGS. 2, 3, and 4 are schematic side elevations of other embodiments ofthe invention.

.Iadd.DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION.Iaddend.

A lens embodying the invention as shown in FIGS. 1 and 1a comprises fromthe object end thirteen elements L1-L13 in four groups G1-G4.

Group G1 comprises a negative meniscus L1, a biconvex element L2, apositive meniscus L3, and is of overall positive power.

Group G2 comprises a negative meniscus L4, a biconcave element L5, and arelatively thick positive doublet shown as a biconvex element L6, and anegative element L7. The doublet L6, L7 is convex to the object and hasa large radius image side surface which may be convex or concave to theimage as shown by the prescriptions, infra.

Group G3, as shown in FIG. 1, comprises a single element L8 very closelyspaced to the aperture defining means or iris I. Component L8 is convexto the object and has an image side surface defined on a very largeradius R_(I) relative to the object side radius R_(o).

Group G4 comprises a biconvex element L9, a relatively thick biconcaveelement L10, a positive meniscus L11 convex to the image, a biconvexelement L12, and a negative meniscus convex to the image.

As will hereinafter be made apparent, the third group bears a certainrelationship to other parameters of the lens:

    0.3<(K.sub.3 /K.sub.G Z.sub.R)<0.15

where

K₃ is the optical power of the group G3

Z_(R) is the zoom ratio of the lens, and

K_(G) is the geometric mean power of the lens, and

K_(G) =√K_(L) K_(S)

where

K_(L) is the power of the lens at the longest equivalent focal length,and

K_(S) is the power of the lens at the shortest equivalent focal length.

Three examples of the lenses substantially as shown in FIGS. 1 and 1aare set forth in Tables I-III. In these examples and as shown in FIGS. 1and 1a, groups G1 and G4 move together toward the object as the EFLincreases, group G2 moves toward the image and group G3 and the aperturedefining means remains stationary with respect to the focal plane FP.

In the following three examples, the prescriptions are for lenses havinga 24×36 mm image frame; an equivalent focal length (EFL) range of 28.6mm to 87.0 mm; and relative apertures which vary from f/2.9 to f/3.9from the lower EFL to the higher EFL.

In Tables I-III, the lens elements are identified from the object to theimage end by L1-L13, the lens element surfaces are S1-S25, the index ofrefraction is N_(D), and the lens element dispersion as measured by theAbbe Number is V_(D). The movements of the various groups are shown bythe data under the heading Zoom Data for various EFL's, Z1, Z2 and Z3are the axial spaces between groups as shown on the drawings. FVD is thefront vertex distance of the lens, and BFL is the back focal length ofthe lens. The relative aperture at the various EFL's is given under theheading f/No.

                  TABLE I                                                         ______________________________________                                                       Surface   Axial Distance                                                      Radius    Between Surfaces                                     Lens  Surface  (mm)      (mm)        N.sub.d                                                                            V.sub.d                             ______________________________________                                              S1       878.67                                                         L1                       3.00        1.805                                                                              25.5                                      S2       53.00                                                                                   1.80                                                       S3       54.94                                                          L2                       8.70        1.786                                                                              43.9                                      S4       -295.19                                                                                 0.15                                                       S5       49.87                                                          L3                       4.30        1.835                                                                              43.0                                      S6       100.18                                                                                  Z1                                                         S7       83.91                                                          L4                       2.00        1.850                                                                              32.2                                      S8       17.34                                                                                   4.80                                                       S9       -116.10                                                        L5                       2.00        1.835                                                                              43.0                                      S10      33.18                                                                                    .20                                                       S11      25.25                                                          L6                       11.54       1.728                                                                              28.3                                      S12      -17.23                                                         L7                       1.50        1.835                                                                              43.0                                      S13      -826.07                                                                                 Z2                                                         aperture                                                                                         1.00                                                       S14      55.92                                                          L8                       2.23        1.667                                                                              48.3                                      S15      1165.66                                                                                 Z3                                                         S16      28.44                                                          L9                       4.79        1.613                                                                              58.6                                      S17      -41.59                                                                                  0.79                                                       S18      -28.11                                                         L10                      12.00       1.593                                                                              35.6                                      S19      38.61                                                                                   2.68                                                       S20      -145.85                                                        L11                      3.00        1.835                                                                              43.0                                      S21      -31.12                                                                                  0.20                                                       S22      51.53                                                          L12                      5.97        1.573                                                                              42.6                                      S23      -23.68                                                                                  0.99                                                       S24      21.43                                                          L13                      1.60        1.805                                                                              25.5                                      S25      -993.13                                                        ______________________________________                                        ZOOM DATA                                                                     f/No. EFL    FVD     Z1     Z2     Z3     BFL                                 ______________________________________                                        2.9   28.6   156.4    .80 mm                                                                              15.3 mm                                                                              14.7 mm                                                                              43.6 mm                                   mm     mm                                                               3.1   40.0   161.3   10.4   10.4   10.3   48.5                                3.5   55.0   165.0   18.6    6.5    6.0   53.1                                3.9   87.0   171.7   29.2    1.0    0.8   58.9                                ______________________________________                                    

                  TABLE II                                                        ______________________________________                                                       Surface   Axial Distance                                                      Radius    Between Surfaces                                     Lens  Surface  (mm)      (mm)        N.sub.d                                                                            V.sub.d                             ______________________________________                                              S1       649.67                                                         L1                       3.00        1.805                                                                              25.5                                      S2       57.37                                                                                   1.80                                                       S3       58.75                                                          L2                       8.70        1.700                                                                              47.8                                      S4       -237.36                                                                                 0.15                                                       S5       52.91                                                          L3                       4.30        1.834                                                                              37.3                                      S6       120.92                                                                                  Z1                                                         S7       70.22                                                          L4                       2.00        1.805                                                                              25.5                                      S8       17.07                                                                                   5.10                                                       S9       -64.49                                                         L5                       2.00        1.589                                                                              61.3                                      S10      25.54                                                                                   0.50                                                       S11      22.97                                                          L6                       7.17        1.699                                                                              30.1                                      S12      -18.35                                                         L7                       7.17        1.699                                                                              30.1                                      S13      158.15                                                                                  Z2                                                         aperture                                                                                         1.30                                                       S14      61.35                                                          L8                       2.23        1.723                                                                              38.0                                      S15      -697.26                                                                                 Z3                                                         S16      31.91                                                          L9                       4.79        1.658                                                                              57.3                                      S17      -40.93                                                                                  0.60                                                       S18      -28.41                                                         L10                      13.30       1.593                                                                              35.5                                      S19      40.69                                                                                   2.84                                                       S10      - 65.65                                                        L11                      3.00        1.583                                                                              46.5                                      S21      -27.15                                                                                  0.20                                                       S22      50.97                                                          L12                      7.25        1.517                                                                              52.2                                      S23      -23.28                                                                                  1.79                                                       S24      -20.86                                                         L13                      1.60        1.847                                                                              23.8                                      S25      -56.24                                                         ______________________________________                                        ZOOM DATA                                                                     f/No. EFL    FVD     Z1     Z2     Z3     BFL                                 ______________________________________                                        2.9   28.6   156.5    0.8 mm                                                                              15.1 mm                                                                              16.4 mm                                                                              42.5 mm                                   mm     mm                                                               3.2   40.0   161.8   10.6   20.4   11.3   47.8                                3.5   55.0   166.7   19.0    6.7    6.6   52.8                                4.0   87.0   173.3   29.8    1.8    0.8   59.3                                ______________________________________                                    

                  TABLE III                                                       ______________________________________                                                       Surface   Axial Distance                                                      Radius    Between Surfaces                                     Lens  Surface  (mm)      (mm)        N.sub.d                                                                            V.sub.d                             ______________________________________                                              S1       367.16                                                         L1                       3.00        1.805                                                                              25.5                                      S2       53.15                                                                                   1.80                                                       S3       54.36                                                          L2                       8.90        1.700                                                                              47.8                                      S4       -220.65                                                                                 0.15                                                       S5       46.30                                                          L3                       4.00        1.834                                                                              37.3                                      S6       83.28                                                                                   Z1                                                         S7       59.28                                                          L4                       2.00        1.805                                                                              25.5                                      S8       16.09                                                                                   5.04                                                       S9       -59.80                                                         L5                       2.00        1.609                                                                              59.2                                      S10      28.34                                                                                   0.50                                                       S11      23.44                                                          L6                       8.00        1.699                                                                              30.1                                      S12      -17.37                                                         L7                       1.50        1.804                                                                              46.5                                      S13      110.83                                                                                  Z2                                                         aperture                                                                                         1.30                                                       S14      63.48                                                          L8                       2.00        1.834                                                                              37.3                                      S15      -659.47                                                                                 Z3                                                         S16      32.68                                                          L9                       4.79        1.661                                                                              57.0                                      S17      -42.95                                                                                  0.60                                                       S18      -29.12                                                         L10                      12.32       1.593                                                                              35.5                                      S19      43.26                                                                                   3.27                                                       S20      - 229.66                                                       L11                      3.80        1.543                                                                              46.9                                      S21      -29.26                                                                                  0.20                                                       S22      57.54                                                          L12                      7.65        1.517                                                                              52.2                                      S23      -24.09                                                                                  1.54                                                       S24      -21.66                                                         L13                      1.80        1.847                                                                              23.8                                      S25      -68.41                                                         ______________________________________                                        ZOOM DATA                                                                     f/No. EFL    FVD     Z1     Z2     Z3     BFL                                 ______________________________________                                        2.9   28.6   156.3    0.84 mm                                                                             13.30 mm                                                                             17.20 mm                                                                             42.3 mm                                   mm     mm                                                               3.2   48.0   161.8   10.32   9.14  11.89  47.8                                3.5   55.0   167.0   18.36   5.95   7.03  53.0                                4.0   87.0   174.3   28.70   1.78   .86   60.3                                ______________________________________                                    

In the foregoing prescriptions, the front vertex distance (FVD) iscalculated from a plane 6.5 mm in front of surfaces S1 when the lensesare focused to a magnification of 1:50.

The lenses set forth in Tables 1-III are so designed that the first andfourth groups move in the same direction for zooming. For simplicity ofmechanical design of the zooming mechanism and to reduce the requiredsize of the front group, the various lens groups move in fixed relationfor focusing. Also the groups G1 and G4 move in fixed relation whenzooming.

In the foregoing lens examples, the third group is in simplest form, asingle element. In the given examples, the object side surface isconvex, and on a much larger radius than the image side surface.##EQU1## where R_(I) is the radius of the image side surface and R_(o)is the radius of the object side surface.

FIGS. 2, 3, and 4 illustrate other embodiments of the invention wherethe third group at the aperture defining means is in the form of an airspaced doublet. FIG. 2 exemplifies the lens with the groups positionedtoward its shorter EFL. The lens comprises elements L1-L6. ElementsL1-L3 define a first positive group G1, elements L4-L8 define a secondnegative group G2. The aperture defining iris D is closely spaced to thethird positive group G3 comprising elements L9 and L10. A fourthpositive group is defined by elements L11-L16.

Group G1 has the same configuration as in examples I-III. Group G2 isagain strongly negative, the forwardmost component is a doublet L4, L5with the overall shape of a negative meniscus, followed by a biconcaveelement L6 and a positive doublet L7, L8. The third group G3 follows theaperture defining iris D and comprises a meniscus 19 air spaced from abiconvex element L10. Group G4 comprises a positive element L11, adoublet L12, L13, a biconvex doublet L14, L15, and a negative meniscusL16 concave to the object.

In the lens of FIG. 2, the third group G3 moves in fixed relation withthe aperture defining iris D during variation in EFL. As the EFL isincreased group G4 moves toward the object end, group G2 moves towardthe image end, group G3 and the iris move in fixed relation toward theobject, and group G1 moves toward the object.

The lens of FIG. 2 as scaled to an image frame of 24×36 mm for an EFLrange of 25.5 mm to 124.0 mm is substantially described in Table IV.

                  TABLE IV                                                        ______________________________________                                                       Surface   Axial Distance                                                      Radius    Between Surfaces                                     Lens  Surface  (mm)      (mm)        N.sub.d                                                                            V.sub.d                             ______________________________________                                              S1       143.67                                                         L1                       3.00        1.805                                                                              25.5                                      S2       45.42                                                                                   0.03                                                       S3       45.12                                                          L2                       13.33       1,476                                                                              70.4                                      S4       -417.52                                                                                 0.10                                                       S5       43.91                                                          L3                       6.94        1.868                                                                              41.2                                      S6       143.05                                                                                  Z1                                                         S7       99.50                                                          L4                       2.00        1.860                                                                              22.8                                      S8       -85.74                                                         L5                       1.50        1.856                                                                              40.0                                      S9       12.47                                                                                   5.26                                                       S10      -41.14                                                         L6                       2.00        1.847                                                                              44.5                                      S11      36.97                                                                                   0.20                                                       S12      23.01                                                          L7                       6.81        1.711                                                                              26.7                                      S13      -13.81                                                         L8                       2.00        1.836                                                                              31.1                                      S14      -91.05                                                                                  Z2                                                         aperture                                                                                         1.50                                                       S15      29.03                                                          L9                       1.63        1.847                                                                              23.8                                      S16      23.58                                                                                   3.32                                                       S17      38.96                                                          L10                      4.55        1.487                                                                              70.4                                      S18      -40.98                                                                                  Z3                                                         S19      39.92                                                          L11                      6.00        1.487                                                                              70.4                                      S10      -109.09                                                                                 0.50                                                       S21      32.42                                                          L12                      8.48        1.465                                                                              65.8                                      S22      -173.96                                                        L13                      2.00        1.600                                                                              38.4                                      S23      29.36                                                                                   1.86                                                       S24      54.84                                                          L14                      2.05        1.835                                                                              63.0                                      S25      19.80                                                          L15                      11.48       1.465                                                                              65.8                                      S26      -20.07                                                                                  0.79                                                       S27      -18.95                                                         L16                      2.50        1.835                                                                              63.0                                      S28      -34.13                                                         ______________________________________                                        ZOOM DATA                                                                     f/No. EFL    FVD     Z1     Z2     Z3     BFL                                 ______________________________________                                        3.4    25.5  179.0    1.00 mm                                                                             17.58 mm                                                                             16.54 mm                                                                             39.0 mm                                   mm     mm                                                               4.1    40.0  179.6    9.53  11.05  13.26  51.0                                4.2    85.0  185.4   28.96   5.68   1.44  54.5                                4.6   124.0  190.9   34.31   1.25   1.53  59.0                                ______________________________________                                    

Another lens embodying the invention is shown in FIG. 3 and comprisesthirteen elements L1-L13 in four groups G1-G4. Group G1 compriseselements L1-L3 in the same positive configurations. Group G2 compriseselements L4-L7 in the same general negative configuration as FIG. 1.Group G3 is a positive doublet L8 and L9 in fixed relation to anaperture defining iris I. Group G4 comprises a positive element L10, abiconvex doublet L11, L12 and a negative meniscus concave to the object.Group G4 is of positive power.

Two examples of the lens as shown in FIG. 3 are set forth in Tables Vand VI. Both lenses are scaled to an EFL range of 24.5 to 124 mm for a24×36 mm image frame. In both lenses, the relative aperture varies fromf/3.6 at the shorter EFL to F/4.7 at the larger EFL. In both of Tables Vand VI, group G3 and the iris I remain stationary. Group G1 moves towardthe object end as the EFL is increased, group G2 moves toward the imageend, and group G4 moves toward the object end. Group G1 moves forfocusing.

                                      TABLE V                                     __________________________________________________________________________              Surface Radius                                                                        Axial Distance Between                                      Lens                                                                              Surface                                                                             (mm)    Surfaces (mm)                                                                             N.sub.d                                                                           V.sub.d                                     __________________________________________________________________________        S1    169.45                                                              L1                3.00        1.805                                                                             25.5                                            S2    56.72                                                                                 0.41                                                            S3    56.53                                                               L2                12.60       1.487                                                                             70.4                                            S4    -605.21                                                                               0.10                                                            S5    54.35                                                               L3                6.9         1.834                                                                             37.3                                            S6    151.66                                                                                Z1                                                              S7    95.83                                                               L4                1.50        1.834                                                                             37.3                                            S8    14.79                                                                                 7.53                                                            S9    -65.44                                                              L5                2.00        1.835                                                                             63.0                                            S10   42.84                                                                                 0.20                                                            S11   27.06                                                               L6                15.72       1.741                                                                             27.8                                            S12   -26.96                                                              L7                1.53        1.773                                                                             49.6                                            S13   -508.18                                                                               Z2                                                              aperture                                                                      S14   33.47                                                               L8                1.50        1.847                                                                             23.8                                            S15   25.18                                                                                 2.66                                                            S16   32.36                                                               L9                4.55        1.487                                                                             70.4                                            S17   -58.18                                                                                Z3                                                              S18   38.94                                                               L10               6.00        1.564                                                                             60.8                                            S19   1862.11                                                                               10.93                                                           S20   94.60                                                               L11               2.00        1.850                                                                             32.2                                            S21   22.04                                                               L12               11.50       1.471                                                                             67.3                                            S22   -25.15                                                                  S23   -21.83                                                              L13               2.00        1.620                                                                             60.3                                            S24   -47.40                                                              __________________________________________________________________________    ZOOM DATA                                                                     f/No.                                                                             EFL   FVD  Z1    Z2    Z3    BFL                                          __________________________________________________________________________    3.6  25.5 mm                                                                            198.8 mm                                                                            1.000 mm                                                                           28.636 mm                                                                           27.353 mm                                                                           40.0 mm                                      4.0  40.0 198.3                                                                              12.482                                                                              16.261                                                                              13.378                                                                              44.6                                         4.6  85.0 214.1                                                                              37.390                                                                               5.983                                                                               2.061                                                                              67.1                                         4.7 124.0 220.1                                                                              47.590                                                                               .874  .700 69.3                                         __________________________________________________________________________

                                      TABLE VI                                    __________________________________________________________________________              Surface Radius                                                                        Axial Distance Between                                      Lens                                                                              Surface                                                                             (mm)    Surfaces (mm)                                                                             N.sub.d                                                                           V.sub.d                                     __________________________________________________________________________        S1    188.72                                                              L1                3.00        1.806                                                                             25.5                                            S2    56.11                                                                                 0.38                                                            S3    56.11                                                               L2                12.20       1.487                                                                             70.4                                            S4    -608.85                                                                 S5    55.24                                                               L3                6.94        1.834                                                                             37.3                                            S6    172.29                                                                                Z1                                                              S7    99.95                                                               L4                1.50        1.834                                                                             37.3                                            S8    14.45                                                                                 6.83                                                            S9    -63.20                                                              L5                2.00        1.835                                                                             43.0                                            S10   42.33                                                                                 0.20                                                            S11   26.50                                                               L6                14.48       1.761                                                                             26.8                                            S12   -28.98                                                              L7                1.53        1.743                                                                             49.2                                            S13   -699.54                                                                               Z2                                                              aperture                                                                                    2.05                                                            S14   33.36                                                               L8                1.50        1.847                                                                             23.8                                            S15   24.83                                                                                 2.50                                                            S16   31.37                                                               L9                4.55        1.762                                                                             26.9                                            S17   -56.74                                                                                Z3                                                              S18   38.07                                                               L10               6.00        1.570                                                                             60.1                                            S19   1365.55                                                                               11.47                                                           S20   88.72                                                               L11               2.00        1.850                                                                             32.2                                            S21   21.05                                                               L12               11.50       1.471                                                                             67.3                                            S22   -25.14                                                                                1.47                                                            S23   -21.79                                                              L13               2.00        1.591                                                                             63.0                                            S24   -47.99                                                              __________________________________________________________________________    ZOOM LENS                                                                     f/No.                                                                             EFL   FVD  Z1    Z2    Z3    BFL                                          __________________________________________________________________________    3.6  25.5 mm                                                                            194.6 mm                                                                            0.800 mm                                                                           26.957 mm                                                                           27.515 mm                                                                           40.1 mm                                      4.0  40.0 194.8                                                                              12.491                                                                              15.244                                                                              13.209                                                                              54.7                                         4.6  85.0 212.2                                                                              38.085                                                                               5.614                                                                               1.817                                                                              67.4                                         4.7 124.0 219.0                                                                              48.820                                                                               0.874                                                                               0.700                                                                              69.4                                         __________________________________________________________________________

FIG. 4 exemplifies another lens form comprising four groups G1-G4. GroupG1 comprises elements L1-L3. Group G2 comprises a negative doublet L4,L5 in the overall shape of a meniscus, a biconcave element L6, and apositive doublet L7, L8. Group G2 is of overall negative power. Group G3comprises a positive doublet L9, L10 closely spaced behind aperturedefining iris D. Group G4 comprises a biconvex element L11, a doubletL12, L13, and a triplet L14, L15, L16 of overall biconvex shape. GroupG4 is of positive power.

Two lenses as shown in FIG. 4 are described in Table VII and Table VIIIas scaled to an EFL range of 24.5 to 124 mm for an image frame of 24×36mm.

                  TABLE VII                                                       ______________________________________                                                      Surface   Axial Distance                                                      Radius    Between Surfaces                                      Lens Surface  (mm)      (mm)       N.sub.d                                                                             V.sub.d                              ______________________________________                                             S1       131.80                                                          L1                      3.00       1.805 25.5                                      S2       45.99                                                                                   0.40                                                       S3       45.95                                                           L2                      13.33      1.487 70.4                                      S4       -352.60                                                                                 0.10                                                       S5       44.42                                                           L3                      6.94       1.806 40.7                                      S6       145.11                                                                                  Z1                                                         S7       138.87                                                          L4                      2.00       1.847 23.8                                      S8       -78.66                                                          L5                      1.50       1.834 37.3                                      S9       13.60                                                                                   5.26                                                       S10      -53.44                                                          L6                      2.00       1.835 43.0                                      S11      29.14                                                                                   0.20                                                       S12      20.88                                                           L7                      10.12      1.717 29.5                                      S13      -12.94                                                          L8                      2.00       1.806 40.7                                      S14      -475.25                                                                                 Z2                                                         aperture                                                                                         1.50                                                       S15      32.75                                                           L9                      1.50       1.805 25.5                                      S16      24.09                                                                                   1.41                                                       S17      31.62                                                           L10                     4.55       1.487 70.4                                      S18      -44.76                                                                                  Z3                                                         S19      42.56                                                           L11                     6.00       1.487 70.4                                      S20      - 72.65                                                                                 0.20                                                       S21      29.20                                                           L12                     10.00      1.487 70.4                                      S22      -42.37                                                          L13                     2.00       1.548 45.8                                      S23      24.84                                                                                   2.00                                                       S24      50.95                                                           L14                     2.05       1.786 43.9                                      S25      18.30                                                           L15                     11.00      1.511 60.5                                      S26      -18.72                                                          L16                     2.00       1.806 40.7                                      S27      -50.49                                                          ______________________________________                                        ZOOM DATA                                                                     f/No.                                                                              EFL      FVD     Z1     Z2     Z3     BFL                                ______________________________________                                        3.8  25.5     185.0   1.000  11.408 37.476 38.5                                    mm       mm      mm     mm     mm     mm                                 4.3  40.0     185.0   9.669  6.664  23.055 49.0                               4.5  85.0     185.0   29.817 3.579  5.742  49.2                               4.0  124.0    185.0   35.019 0.150  0.401  52.8                               ______________________________________                                    

                  TABLE VIII                                                      ______________________________________                                                      Surface   Axial Distance                                                      Radius    Between Surfaces                                      Lens Surface  (mm)      (mm)       N.sub.d                                                                             V.sub.d                              ______________________________________                                             S1       142.69                                                          L1                      3.00       1.805 25.5                                      S2       46.13                                                                                   0.40                                                       S3       46.01                                                           L2                      13.33      1.487 70.4                                      S4       -487.79                                                                                 0.10                                                       S5       44.75                                                           L3                      6.94       1.806 40.7                                      S6       145.88                                                                                  Z1                                                         S7       106.19                                                          L4                      2.00       1.847 23.8                                      S8       -73.61                                                          L5                      1.50       1.834 37.3                                      S9       12.93                                                                                   5.26                                                       S10      -49.58                                                          L6                      2.00       1.835 43.0                                      S11      39.03                                                                                   0.20                                                       S12      21.94                                                           L7                      14.07      1.717 29.5                                      S13      -13.02                                                          L8                      2.00       1.806 40.1                                      S14      584.71                                                                                  Z2                                                         Aperture                                                                                         2.05                                                       S15      31.39                                                           L9                      1.50       1.805 25.5                                      S16      23.71                                                                                   1.58                                                       S17      31.06                                                           L10                     4.55       1.487 70.4                                      S18      -51.85                                                                                  Z3                                                         S19      43.25                                                           L11                     6.00       1.487 70.4                                      S20      -70.85                                                                                  0.20                                                       S21      27.36                                                           L12                     10.00      1.487 70.4                                      S22      -43.76                                                          L13                     2.00       1.541 47.2                                      S23      23.42                                                                                   2.00                                                       S24      45.83                                                           L14                     2.05       1.786 43.9                                      S25      16.77                                                           L15                     11.00      1.511 60.5                                      S26      -18.30                                                          L16                     2.00       1.806 40.7                                      S27      -52.02                                                          ______________________________________                                        ZOOM DATA                                                                     f/No.                                                                              EFL      FVD     Z1     Z2     Z3     BFL                                ______________________________________                                        3.8  25.5     179.l   1.00   11.328 26.532 38.5                                    mm       mm      mm     mm     mm     mm                                 4.3  40.0     183.3   9 993  6.959  15.013 50.6                               4.5  85.0     194.9   30.520 3.333  3.717  56.6                               4.6  l24.0    203.1   35.169 0.292  0.500  66.4                               ______________________________________                                    

The lens of Table VII has a relative aperture varying from f/3.8 at theshorter EFL to f/4.6 at the larger EFL. The front vertex distance (FVD)of this lens does not change during zooming. As the .[.FFL.]. .Iadd.EFL.Iaddend.is increased from the lower value, group G2 moves toward theimage end, group G3 and iris D move in fixed relation toward the imageend and group G4 moves toward the object end.

The lens of Table VIII has a relative aperture varying from f/3.8 tof/4.6 at the larger EFL. Here all four groups move during zooming. Asthe EFL is increased, group G1 moves toward the object end, group G2moves toward the image end, group G3 and iris D first move toward theimage end and then reverse and move toward the object end, and group G4moves toward the object.

In the prescriptions of Tables IV-VIII, the front vertex distance (FVD)is calculated from a plane 5.00 mm in front of surfaces 51. In tables IVand VI the lenses are focused for a magnification of 1:40 and in tablesV, VII and VIII the lenses are focused at infinity.

The power of the groups G1-G4 of the various lenses are set forth inTable IX as K₁ -K₄ respectively together with the geometric mean of thepowers K_(G) of the lens at the ERL extremities, and the zoom ratioZ_(R).

                  TABLE IX                                                        ______________________________________                                        TABLE   K.sub.1 K.sub.2  K.sub.3                                                                             K.sub.4                                                                             K.sub.G                                                                             Z.sub.R                            ______________________________________                                        I       .0121   -.0498   .0114 .0224 .020  3.04                               II      .0118   -.0512   .0129 .0220 .020  3.04                               III     .0121   -.0556   .0145 .0223 .020  3.04                               IV      .0143   -.0726   .0182 .0149 .0178 4.86                               V       .0103   -.0521   .0156 .0110 .0178 4.86                               VI      .0137   -.0748   .0177 .0186 .0178 4.86                               VII     .0102   -.0528   .0159 .0115 .0178 4.86                               VIII    .0129   -.0763   .0171 .0189 .0178 4.86                               ______________________________________                                         ##STR1##                                                                     -  where K.sub.L is the power of the lens at its longest EFL and K.sub.S i     the power of the lens at its shortest EFL.

It will be noted from the foregoing examples that the power K₃ of groupG3 is substantially equal to or greater than the power K₁ of the frontgroup G1. Also K₃ is substantially equal to or less than the geometricmean power K_(G) of the lens at the extremes of its EFL range.

The power K₃ of group G3 as shown above bears certain relationships toother parameters of the lens:

    1.2>(K.sub.3 /K.sub.G)>0.4

    0.006>(K.sub.3 /Z.sub.R)>0.003

    0.25>(K.sub.3 /K.sub.G Z.sub.R)>0.15

The third group G3 may be placed on either side of the iris; however, inmost cases to permit movement of the other groups to provide thesmallest FVD, it will be very closely spaced to the image side of theiris.

While preferred embodiments of the invention have been described,alternate embodiments, as well as other embodiments of the invention mayoccur to those skilled in the art. Accordingly, the appended claims areintended to encompass all modifications and embodiments of the inventionwhich do not depart from the spirit and scope of the invention.

What I claim is:
 1. A lens of variable equivalent focal length.Iadd.extending from a dimension below the diagonal of the image frameof the lens to a dimension substantially above .Iaddend.comprising fromthe object end a first positive group, a second negative group, anaperture defining means, a third positive group closely spaced in fixedrelation to the aperture defining means, and a fourth positive group,said .[.second.]. .Iadd.first .Iaddend.and fourth groups being movable.Iadd.in the same direction .Iaddend.to vary the equivalent focal lengthof the lens, .Iadd.while said second group moves in the oppositedirection, .Iaddend.said third group and said aperture defining meansremaining stationary during change in equivalent focal length.Iadd.,said second group being of strong negative optical power, and
 5. 0>|K₂/K_(G) |>2.0where K₂ is the optical power of said second group and K_(G)is the geometric mean of the powers of said lens at the extremes of itsequivalent focal lengths. .Iaddend. .[.2. The lens of claim 1 whereinsaid first group also moves to vary the equivalent focal length of saidlens..].
 3. The lens of claim .[.2.]. .Iadd.1 .Iaddend.wherein saidfirst and fourth groups move in fixed relation.
 4. The lens of claim 1where all of said groups move in fixed relation to focus said lens. 5.The lens of claim 1 wherein said third group comprises a single elementand ##EQU2## where the image side surface of said element is defined ona radius R_(I) and the object side surface of said element is defined ona radius R_(o).
 6. The lens of claim 1 wherein said third groupcomprises two elements.
 7. The lens of claim 6 wherein said third groupcomprises a negative meniscus and a biconvex element.
 8. The lens ofclaim 1 wherein:

    0.3>K.sub.3 /K.sub.G Z.sub.R >0.15

where K₃ is the power of the third group K_(G) is the geometric mean ofthe powers of the lens at the extremes of its focal length range, andZ_(R) is the zoom ratio of the lens.
 9. The lens of claim 1 wherein:

    1.3>K.sub.3 /K.sub.G >0.4

where K₃ is the power of the third group, and K_(G) is the geometricmean of the powers of the lens at the extremes of its focal lengthrange. .[.10. In a lens of variable focal length, of the type where anegative group on the object side of an aperture defining means and apositive group on the image side of the aperture defining means moveaxially with respect to the aperture defining means to vary theequivalent focal length of the lens, the improvement comprising, apositive lens component closely, positioned to said aperture definingmeans and in fixed relation thereto; said aperture defining means andsaid positive lens component remaining stationary during variation ofthe equivalent focal length..]. .[.11. The lens of claim 10 wherein:

    0.3>K.sub.3 /K.sub.G Z.sub.R >0.15

where K₃ is the power of said positive lens component K_(G) is thegeometric means of the powers of the lens at the extremes of its focallength range, and Z_(R) is the zoom ratio of the lens..]. .[.12. Thelens of claim 10 wherein:

    1.3>K.sub.3 /K.sub.G >0.4..].


13. The lens of claim 1 where the power of said positive group in fixedrelation to the aperture defining means is substantially equal to orgreater than the power of said front group.
 14. The lens of claim 1where the power of said positive group in fixed relation to the aperturedefining means is substantially equal to or less than the geometric meanpower of said lens.
 15. The lens of claim 1 where the power of saidthird group is substantially equal to or greater than the power of saidfirst group and substantially equal to or less .[.then.]. .Iadd.than.Iaddend.the geometric mean of the powers of the lens at the extremes ofits equivalent focal lengths.
 16. A zoom lens .Iadd.having a range ofequivalent focal lengths from a dimension below the diagonal of theimage frame of said lens to substantially above .Iaddend.comprisingmeans defining a variable aperture, a first positive and a secondnegative lens group on the object side of said aperture defining means,.Iadd.and .Iaddend.a .Iadd.rear .Iaddend.positive group on the imageside of said aperture defining means, said .Iadd.first, second and rear.Iaddend.lens groups being axially movable with respect to said aperturedefining means to vary the equivalent focal length of said lens and athird positive group closely positioned to said aperture defining meansand in fixed relation thereto, said third group being stationary as saidother groups are moved to vary the equivalent focal length, all of saidgroups being movable in fixed relation to focus said lens.
 17. The lensof claim 16 wherein said positive group on the object side of saidnegative group and said positive group on the image side of saidaperture defining means move in fixed relation with variation inequivalent focal length.
 18. The lens of claim 16 where the group infixed relation to said aperture defining means has an optical power K₃,the geometric mean power of said lens is K_(G), and lens has a zoomratio Z_(R), and

    0.25>K.sub.3 /K.sub.G Z.sub.R >0.15

.Iadd.and where K₃ is the optical power of said third group, K_(G) isthe geometric mean of the optical powers of said lens at the extremes ofits equivalent focal length range and Z_(R) is the zoom ratio of saidlens. .Iaddend.
 19. The lens of claim 16 where

    0.006>K.sub.3 /Z.sub.R >0.003

.Iadd.where K₃ is the optical power of said lens expressed as thereciprocal of its equivalent focal length in millimeters, and Z_(R) isthe zoom ratio of said lens. .Iaddend.
 20. The lens of claim 16 where

    1.2>K.sub.3 /K.sub.G >0.4

.Iadd.and where K₃ is the optical power of said third group, and K_(G)is the geometric mean of the optical powers of said lens at the extremesof its equivalent focal length range. .Iaddend.
 21. A lens according toclaim 1 as scaled to an equivalent focal length of 28.5 to 87.0 mm for a24×36 mm image frame defined substantially as follows:

    ______________________________________                                                       Surface   Axial Distance                                                      Radius    Between Surfaces                                     Lens  Surface  (mm)      (mm)        N.sub.d                                                                            V.sub.d                             ______________________________________                                              S1       878.67                                                         L1                       3.00        1.805                                                                              25.5                                      S2       53.00                                                                                   1.80                                                       S3       54.94                                                          L2                       8.70        1.786                                                                              43.9                                      S4       -295.19                                                                                 0.15                                                       S5       49.87                                                          L3                       4.30        1.835                                                                              43.0                                      S6       100.18                                                                                  Z1                                                         S7       83.91                                                          L4                       2.00        1.850                                                                              32.2                                      S8       17.34                                                                                   4.80                                                       S9       -116.10                                                        L5                       2.00        1.835                                                                              43.0                                      S10      33.18                                                                                    .20                                                       S11      25.25                                                          L6                       11.54       1.728                                                                              28.3                                      S12      -17.23                                                         L7                       1.50        1.835                                                                              43.0                                      S13      -826.07                                                                                 Z2                                                         aperture                                                                                         1.00                                                       S14      55.92                                                          L8                       2.23        1.667                                                                              48.3                                      S15      1165.66                                                                                 Z3                                                         S16      28.44                                                          L9                       4.79        1.613                                                                              58.6                                      S17      -41.59                                                                                  0.79                                                       S18      -28.11                                                         L10                      12.00       1.593                                                                              35.6                                      S19      38.61                                                                                   2.68                                                       S20      -145.85                                                        L11                      3.00        1.835                                                                              43.0                                      S21      -31.12                                                                                  0.20                                                       S22      51.53                                                          L12                      5.97        1.573                                                                              42.6                                      S23      -23.68                                                                                  0.99                                                       S24      21.43                                                          L13                      1.60        1.805                                                                              25.5                                      S25      -993.13                                                        ______________________________________                                        ZOOM DATA                                                                     EFL     FVD      Z1       Z2     Z3     BFL                                   ______________________________________                                        28.6 mm 156.4 mm  .80 mm  15.3 mm                                                                              14.7 mm                                                                              43.6                                  40.0    161.3    10.4     10.4   10.3   48.5                                  55.0    165.0    18.6      6.5    6.0   53.1                                  87.0    171.7    29.2      1.0    0.8   58.9                                  ______________________________________                                    

where L1-L13 are lens elements from the object end; S1-S15 are the lenssurfaces from the object end with positive radii struck from the rightand negative .[.ratii.]. .Iadd.radii .Iaddend.struck from the left;N_(d) is the index of refraction of the lens element; V_(d) is the Abbenumber of the lens elements; Z1, Z2 and Z3 are variable during change inequivalent focal length; EFL is the equivalent focal length; FVD is thefront vertex distance; and BFL is the back focal length.
 22. A lensaccording to claim 1 as scaled to an equivalent focal length of 28.5 to87.0 mm for a 24×36 mm image frame defined substantially as follows:

    ______________________________________                                                       Surface   Axial Distance                                                      Radius    Between Surfaces                                     Lens  Surface  (mm)      (mm)        N.sub.d                                                                            V.sub.d                             ______________________________________                                              S1       649.67                                                         L1                       3.00        1.805                                                                              25.5                                      S2       57.37                                                                                   1.80                                                       S3       58.75                                                          L2                       8.70        1.700                                                                              47.8                                      S4       -237.36                                                                                 0.15                                                       S5       52.91                                                          L3                       4.30        1.834                                                                              37.3                                      S6       120.92                                                                                  Z1                                                         S7       70.22                                                          L4                       2.00        1.805                                                                              25.5                                      S8       17.07                                                                                   5.10                                                       S9       -64.49                                                         L5                       2.00        1.589                                                                              61.3                                      S10      25.54                                                                                   0.50                                                       S11      22.97                                                          L6                       7.17        1.699                                                                              30.1                                      S12      -18.35                                                         L7                       7.17        1.699                                                                              30.1                                      S13      158.15                                                                                  Z2                                                         aperture                                                                                         1.30                                                       S14      61.35                                                          L8                       2.23        1.723                                                                              38.0                                      S15      -697.26                                                                                 Z3                                                         S16      31.91                                                          L9                       4.79        1.658                                                                              57.3                                      S17      -40.93                                                                                  0.60                                                       S18      -28.41                                                         L10                      13.30       1.593                                                                              35.5                                      S19      40.69                                                                                   2.84                                                       S10      -65.65                                                         L11                      3.00        1.583                                                                              46.5                                      S21      -27.15                                                                                  0.20                                                       S22      50.97                                                          L12                      7.25        1.517                                                                              52.2                                      S23      -23.28                                                                                  1.79                                                       S24      -20.86                                                         L13                      1.60        1.847                                                                              23.8                                      S25      -56.24                                                         ______________________________________                                        ZOOM DATA                                                                     EFL     FVD      Z1       Z2     Z3     BFL                                   ______________________________________                                        28.6 mm 156.5 mm  0.8 mm  15.1 mm                                                                              16.4 mm                                                                              42.5 mm                               40.0    161.8    10.6     20.4   11.3   47.8                                  55.0    166.7    19.0      6.7    6.6   52.8                                  87.0    173.3    29.8      1.8    0.8   59.3                                  ______________________________________                                    

where L1-L13 are lens elements from the object end; S1-S25 are the lenssurfaces from the object end with positive radii struck from the rightand negative radii struck from the left; N_(d) is the index ofrefraction of the lens elements; V_(d) is the Abbe number of the lenselements; Z1, Z2 and Z3 are variable during change in equivalent focallength; EFL is the equivalent focal length; FVD is the front vertexdistance; and BFL is the back focal length.
 23. A lens according toclaim 1 as scaled to an equivalent focal length of 28.5 to 87.0 mm for a24×36 mm image frame defined substantially as follows:

    ______________________________________                                                       Surface   Axial Distance                                                      Radius    Between Surfaces                                     Lens  Surface  (mm)      (mm)        N.sub.d                                                                            V.sub.d                             ______________________________________                                              S1       367.16                                                         L1                       3.00        1.805                                                                              25.5                                      S2       53.15                                                                                   1.80                                                       S3       54.36                                                          L2                       8.90        1.700                                                                              47.8                                      S4       -220.65                                                                                 0.15                                                       S5       46.30                                                          L3                       4.00        1.834                                                                              37.3                                      S6       83.28                                                                                   Z1                                                         S7       59.28                                                          L4                       2.00        1.805                                                                              25.5                                      S8       16.09                                                                                   5.04                                                       S9       -59.80                                                         L5                       2.00        1.609                                                                              59.2                                      S10      28.34                                                                                   0.50                                                       S11      23.44                                                          L6                       8.00        1.699                                                                              30.1                                      S12      -17.37                                                         L7                       1.50        1.804                                                                              46.5                                      S13      110.83                                                                                  Z2                                                         aperture                                                                                         1.30                                                       S14      63.48                                                          L8                       2.00        1.834                                                                              37.3                                      S15      -659.47                                                                                 Z3                                                         S16      32.68                                                          L9                       4.79        1.661                                                                              57.0                                      S17      -42.95                                                                                  0.60                                                       S18      -29.12                                                         L10                      12.32       1.593                                                                              35.5                                      S19      43.26                                                                                   3.27                                                       S20      -229.66                                                        L11                      3.80        1.543                                                                              46.9                                      S21      -29.26                                                                                  0.20                                                       S22      57.54                                                          L12                      7.65        1.517                                                                              52.2                                      S23      -24.09                                                                                  1.54                                                       S24      -21.66                                                         L13                      1.80        1.847                                                                              23.8                                      S25      -68.41                                                         ______________________________________                                        ZOOM DATA                                                                     EFL     FVD      Z1       Z2     Z3     BFL                                   ______________________________________                                        28.6 mm 156.3 mm  0.84 mm 13.30 mm                                                                             17.20 mm                                                                             42.3 mm                               48.0    161.8    10.32     9.14  11.89  47.8                                  55.0    167.0    18.36     5.95   7.03  53.0                                  87.0    174.3    28.70     1.78   .86   60.3                                  ______________________________________                                    

where L1-L13 are lens elements from the object end; S1-S25 are the lenssurfaces from the object end with positive radii struck from the rightand negative radii struck from the left; N_(d) is the index ofrefraction of the lens elements; V_(d) is the Abbe number of the lenselements; Z1, Z2, and Z3 are variable during change in equivalent focallength; EFL is the equivalent focal length; FVD is the front vertexdistance; and BFL is the back focal length.
 24. A lens according toclaim 1 as scaled to an equivalent focal length of 25.5 to 124.0 mm fora 24×36 mm image frame defined substantially as follows:

    ______________________________________                                                       Surface   Axial Distance                                                      Radius    Between Surfaces                                     Lens  Surface  (mm)      (mm)        N.sub.d                                                                            V.sub.d                             ______________________________________                                              S1       143.67                                                         L1                       3.00        1.805                                                                              25.5                                      S2       45.42                                                                                   0.03                                                       S3       45.12                                                          L2                       13.33       1.476                                                                              70.4                                      S4       -417.52                                                                                 0.10                                                       S5       43.91                                                          L3                       6.94        1.868                                                                              41.2                                      S6       143.05                                                                                  Z1                                                         S7       99.50                                                          L4                       2.00        1.860                                                                              22.8                                      S8       -85.74                                                         L5                       1.50        1.856                                                                              40.0                                      S9       12.47                                                                                   5.26                                                       S10      -41.14                                                         L6                       2.00        1.847                                                                              44.5                                      S11      36.97                                                                                   0.20                                                       S12      23.01                                                          L7                       6.81        1.711                                                                              26.7                                      S13      -13.81                                                         L8                       2.00        1.836                                                                              31.1                                      S14      -91.05                                                                                  Z2                                                         aperture                                                                                         1.50                                                       S15      29.03                                                          L9                       1.63        1.847                                                                              23.8                                      S16      23.58                                                                                   3.32                                                       S17      38.96                                                          L10                      4.55        1.487                                                                              70.4                                      S18      -40.98                                                                                  Z3                                                         S19      39.92                                                          L11                      6.00        1.487                                                                              70.4                                      S10      -109.09                                                                                 0.50                                                       S21      32.42                                                          L12                      8.48        1.465                                                                              65.8                                      S22      -173.96                                                        L13                      2.00        1.600                                                                              38.4                                      S23      29.36                                                                                   1.86                                                       S24      54.84                                                          L14                      2.05        1.835                                                                              63.0                                      S25      19.80                                                          L15                      11.48       1.465                                                                              65.8                                      S26      -20.07                                                                                  0.79                                                       S27      -18.95                                                         L16                      2.50        1.835                                                                              63.0                                      S28      -34.13                                                         ______________________________________                                        ZOOM DATA                                                                     EFL     FVD      Z1       Z2     Z3     BFL                                   ______________________________________                                         25.5 mm                                                                              179.0 mm  1.00 mm 17.58 mm                                                                             16.54 mm                                                                             39.0 mm                                40.0   179.6     9.53    11.05  13.26  51.0                                   85.0   185.4    28.96     5.68   1.44  54.5                                  124.0   190.9    34.31     1.25   1.53  59.0                                  ______________________________________                                    

where L1-L16 are lens elements from the object end; S1-S28 are the lenssurfaces from the object end with positive radii struck from the rightand negative radii struck from the left; N_(d) is the index ofrefraction of the lens elements; V_(d) is the Abbe number of the lenselements; Z1, Z2 and Z3 are variable during change in equivalent focallength; EFL is the equivalent focal length; FVD is the front vertexdistance; and BFL is the back focal length.
 25. A lens according toclaim 1 as scaled to an equivalent focal length of 25.5 to 124.0 mm fora 24×36 mm image frame defined substantially as follows:

    __________________________________________________________________________              Surface Radius                                                                        Axial Distance Between                                      Lens                                                                              Surface                                                                             (mm)    Surfaces (mm)                                                                             N.sub.d                                                                           V.sub.d                                     __________________________________________________________________________        S1    169.45                                                              L1                3.00        1.805                                                                             25.5                                            S2    56.72                                                                                 0.41                                                            S3    56.53                                                               L2                12.60       1.487                                                                             70.4                                            S4    -605.21                                                                               0.10                                                            S5    54.35                                                               L3                6.9         1.834                                                                             37.3                                            S6    151.66                                                                                Z1                                                              S7    95.83                                                               L4                1.50        1.834                                                                             37.3                                            S8    14.79                                                                                 7.53                                                            S9    -65.44                                                              L5                2.00        1.835                                                                             63.0                                            S10   42.84                                                                                 0.20                                                            S11   27.06                                                               L6                15.72       1.741                                                                             27.8                                            S12   -26.96                                                              L7                1.53        1.773                                                                             49.6                                            S13   -508.18                                                                               Z2                                                              aperture                                                                      S14   33.47                                                               L8                1.50        1.847                                                                             23.8                                            S15   25.18                                                                                 2.66                                                            S16   32.36                                                               L9                4.55        1.487                                                                             70.4                                            S17   -58.18                                                                                Z3                                                              S18   38.94                                                               L10               6.00        1.564                                                                             60.8                                            S19   1862.11                                                                               10.93                                                           S20   94.60                                                               L11               2.00        1.850                                                                             32.2                                            S21   22.04                                                               L12               11.50       1.471                                                                             67.3                                            S22   -25.15                                                                  S23   -21.83                                                              L13               2.00        1.620                                                                             60.3                                            S24   -47.40                                                              __________________________________________________________________________    ZOOM DATA                                                                     EFL  FVD   Z1     Z2     Z3     BFL                                           __________________________________________________________________________     25.5 mm                                                                           198.8 mm                                                                             1.000 mm                                                                            28.636 mm                                                                            27.353 mm                                                                            40.0 mm                                        40.0                                                                              198.3 12.482 16.261 13.378 44.6                                           85.0                                                                              214.1 37.390  5.983  2.061 67.1                                          124.0                                                                              220.1 47.590  .874   .700  69.3                                          __________________________________________________________________________

where L1-L13 are lens elements from the object end; S1-S24 are the lenssurfaces from the object end with positive radii struck from the rightand negative radii struck from the left; N_(d) is the index ofrefraction of the lens element; V_(d) is the Abbe number of the lenselements; Z1, Z2 and Z3 are variable during change in equivalent focallength; EFL is the equivalent focal length; FVD is the front vertexdistance; and BFL is the back focal length.
 26. A lens according toclaim 1 as scaled to an equivalent focal length of 25.5 to 124.0 mm fora 24×36 mm image frame defined substantially as follows:

    __________________________________________________________________________              Surface Radius                                                                        Axial Distance Between                                      Lens                                                                              Surface                                                                             (mm)    Surfaces (mm)                                                                             N.sub.d                                                                           V.sub.d                                     __________________________________________________________________________        S1    188.72                                                              L1                3.00        1.806                                                                             25.5                                            S2    56.11                                                                                 0.38                                                            S3    56.11                                                               L2                12.20       1.487                                                                             70.4                                            S4    -608.85                                                                 S5    55.24                                                               L3                6.94        1.834                                                                             37.3                                            S6    172.29                                                                                Z1                                                              S7    99.95                                                               L4                1.50        1.834                                                                             37.3                                            S8    14.45                                                                                 6.83                                                            S9    -63.20                                                              L5                2.00        1.835                                                                             43.0                                            S10   42.33                                                                                 0.20                                                            S11   26.50                                                               L6                14.4        1.761                                                                             26.8                                            S12   -28.98                                                              L7                1.53        1.743                                                                             49.2                                            S13   -699.54                                                                               Z2                                                              aperture                                                                                    2.05                                                            S14   33.36                                                               L8                1.50        1.847                                                                             23.8                                            S15   24.83                                                                                 2.50                                                            S16   31.37                                                               L9                4.55        1.762                                                                             26.9                                            S17   -56.74                                                                                Z3                                                              S18   38.07                                                               L10               6.00        1.570                                                                             60.1                                            S19   1365.55                                                                               11.47                                                           S20   88.72                                                               L11               2.00        1.850                                                                             32.2                                            S21   21.05                                                               L12               11.50       1.471                                                                             67.3                                            S22   -25.14                                                                                1.47                                                            S23   21.79                                                               L13               2.00        1.591                                                                             63.0                                            S24   -47.99                                                              __________________________________________________________________________    ZOOM LENS                                                                     EFL  FVD   Z1     Z2     Z3     BFL                                           __________________________________________________________________________     25.5 mm                                                                           194.6 mm                                                                             0.800 mm                                                                            26.957 mm                                                                            27.515 mm                                                                            40.1 mm                                        40.0                                                                              194.8 12.491 15.244 13.209 54.7                                           85.0                                                                              212.2 38.085  5.614  1.817 67.4                                          124.0                                                                              219.0 48.820  0.874  0.700 69.4                                          __________________________________________________________________________

wherein L1-L13 are lens elements from the object end; S1-S24 are thelens surfaces from the object end with positive radii struck from theright and negative radii struck from the left; N_(d) is the index ofrefraction of the lens elements; V_(d) is the Abbe number of the lenselements; Z1, Z2, and Z3 are variable during change in equivalent focallength; EFL is the equivalent focal length; FVD is the front vertexdistance; and BFL is the back focal length.
 27. A lens according toclaim 1 as scaled to an equivalent focal length of 25.5 to 124.0 mm fora 24×36 mm image frame defined substantially as follows:

    ______________________________________                                                      Surface   Axial Distance                                                      Radius    Between Surfaces                                      Lens Surface  (mm)      (mm)       N.sub.d                                                                             V.sub.d                              ______________________________________                                             S1       131.80                                                          L1                      3.00       1.805 25.5                                      S2       45.99                                                                                   0.40                                                       S3       45.95                                                           L2                      13.33      1.487 70.4                                      S4       -352.60                                                                                 0.10                                                       S5       44.42                                                           L3                      6.94       1.806 40.7                                      S6       145.11                                                                                  Zl                                                         S7       138.87                                                          L4                      2.00       1.847 23.8                                      S8       -78.66                                                          L5                      1.50       1.834 37.3                                      S9       13.60                                                                                   5.26                                                       S10      -53.44                                                          L6                      2.00       1.835 43.0                                      S11      29.14                                                                                   0.20                                                       S12      20.88                                                           L7                      10.12      1.717 29.5                                      S13      -12.94                                                          L8                      2.00       1.806 40.7                                      S14      -475.25                                                                                 Z2                                                         aperture                                                                                         1.50                                                       S15      32.75                                                           L9                      1.50       1.805 25.5                                      S16      24.09                                                                                   1.41                                                       S17      31.62                                                           L10                     4.55       1.487 70.4                                      S18      -44.76                                                                                  Z3                                                         S19      42.56                                                           Lll                     6.00       1.487 70.4                                      S20      -72.65                                                                                  0.20                                                       S21      29.20                                                           L12                     10.00      1.487 70.4                                      S22      -42.37                                                          L13                     2.00       1.548 45.8                                      S23      24.84                                                                                   2.00                                                       S24      50.95                                                           L14                     2.05       1.786 43.9                                      S25      18.30                                                           L15                     11.00      1.511 60.5                                      S26      -18.72                                                          L16                     2.00       1.806 40.7                                      S27      -50.49                                                          ______________________________________                                        ZOOM DATA                                                                     EFL    FVD      Z1       Z2      Z3      BFL                                  ______________________________________                                        25.5 mm                                                                              185.0 mm 1.000 mm 11.408 mm                                                                             37.476 mm                                                                             38.5                                                                          mm                                   40.0   185.0    9.669    6.664   23.055  49.0                                 85.0   185.0    29.817   3.579   5.742   49.2                                 124.0  185.0    35.019   0.150   0.401   52.8                                 ______________________________________                                    

where L1-L16 are lens elements from the object end; S1-S27 are the lenssurfaces from the object end with positive radii struck from the rightand negative radii struck from the left; N_(d) is the index ofrefraction of the lens elements; V_(d) is the Abbe number of the lenselements; Z1, Z2, and Z3 are variable during change in equivalent focallength; EFL is the equivalent focal length; FVD is the front vertexdistance; and BFL is the back focal length.
 28. A lens according toclaim 1 as scaled to an equivalent focal length of 25.5 to 124.0 mm fora 24×36 mm image frame defined substantially as follows:

    ______________________________________                                                      Surface   Axial Distance                                                      Radius    Between Surfaces                                      Lens Surface  (mm)      (mm)       N.sub.d                                                                             V.sub.d                              ______________________________________                                             Sl       142.69                                                          Ll                      3.00       1.805 25.5                                      S2       46.13                                                                                   0.40                                                       S3       46.01                                                           L2                      13.33      1.487 70.4                                      S4       -487.79                                                                                 0.10                                                       S5       44.75                                                           L3                      6.94       1.806 40.7                                      S6       145.88                                                                                  Z1                                                         S7       106.19                                                          L4                      2.00       1.847 23.8                                      S8       -73.61                                                          L5                      1.50       1.834 37.3                                      S9       12.93                                                                                   5.26                                                       S10      -49.58                                                          L6                      2.00       1.835'                                                                              43.0                                      S11      39.03                                                                                   0.20                                                       S12      21.94                                                           L7                      14.07      1.717 29.5                                      S13      -13.02                                                          L8                      2.00       1.806 40.1                                      S14      584.71                                                                                  Z2                                                         Aperture                                                                                         2.05                                                       S15      31.39                                                           L9                      1.50       1.805 25.5                                      S16      23.71                                                                                   1.58                                                       S17      31.06                                                           L10                     4.55       1.487 70.4                                      S18      -51.85                                                                                  Z3                                                         S19      43.25                                                           L11                     6.00       1.487 70.4                                      S20      -70.85                                                                                  0.20                                                       S21      27.36                                                           L12                     10.00      1.487 70.4                                      S22      -43.76                                                          L13                     2.00       1.541 47.2                                      S23      23.42                                                                                   2.00                                                       S24      45.83                                                           L14                     2.05       1.786 43.9                                      S25      16.77                                                           L15                     11.00      1.511 60.5                                      S26      -18.30                                                          L16                     2.00       1.806 40.7                                      S27      -52.02                                                          ______________________________________                                        ZOOM DATA                                                                     EFL    FVD      Z1       Z2      Z3      BFL                                  ______________________________________                                        25.5 mm                                                                              179.l mm 1.000 mm 11.328 mm                                                                             26.53 mm                                                                              38.5                                                                          mm                                   40.0   183.3    9.993    6.959   15.013  50.6                                 85.0   194.9    30.520   3.333   3.717   56.6                                 124.0  203.1    35.169   0.292   0.500   66.4                                 ______________________________________                                    

where L1-L16 are lens elements from the object end; S1-S27 are the lenssurfaces from the object end with positive radii struck from the rightand negative radii struck from the left; N_(d) is the index ofrefraction of the lens elements; V_(d) is the Abbe number of the lenselements; Z1, Z2 and Z3 are variable during change in equivalent focallength; EFL is the equivalent length; FVD is the front vertex distance;and BFL is the back focal length.
 29. A lens of variable equivalentfocal length consisting from the object end a first positive group, asecond negative group, a third positive group, and a fourth positivegroup, an aperture defining means closely positioned to said third groupand in fixed relation, said .Iadd.first, .Iaddend.second and fourthgroups being axially movable to vary the equivalent focal length of thelens, said third group and said aperture defining means being stationaryas the equivalent focal length of the lens is varied.
 30. The lens ofclaim 29 where

    0.5<K.sub.1 /K.sub.G <1.0

    2.0<|K.sub.2 /K.sub.G |<5.0

    0.4<K.sub.3 /K.sub.G <1.2

    0.5<K.sub.4 /K.sub.G <1.3

where K₁, K₂, K₃ and K₄ are the powers of said first, second, third andfourth groups respectively, and K_(G) is the geometric mean of thepowers of said lens at the extremes of its equivalent focal lengths. 31.A lens .Iadd.of variable equivalent focal length extending from adimension below the diagonal of the image frame of the lens to adimension substantially above .Iaddend.for a camera having a 24×36 mmimage frame comprising from the object end, a first positive group, asecond negative group, a third positive group, and a fourth positivegroup, said .Iadd.first, .Iaddend.second and fourth groups being movablesimultaneously .[.in opposite directions.]. to vary the equivalent focallength of said lens, .Iadd.said first and fourth groups being movable inthe same direction, .Iaddend.said third lens group being stationary, anaperture defining means closely spaced to said third group and in fixedrelation thereto, and

    0.015>K.sub.1 >0.010

    0.080>|K.sub.2 |>0.040

    0.019>K.sub.3 >0.010

    0.023>K.sub.4 >0.010

where K₁, K₂, K₃, and K₄, are the optical powers of said first, second,third, and fourth groups expressed as the reciprocal of the equivalentfocal lengths in millimeters of said groups.